Process for the preparation of 4-keto-1,2,3,4-tetrahydrocarbazole

ABSTRACT

An improved process for the preparation of 4-keto-1,2,3,4tetrahydrocarbazole is disclosed. This process is as follows:

United States Patent 1 Zinnes PROCESS FOR THE PREPARATION OF 4-KETO-l,2,3,4-TETRAHYDROCARBAZOLE [75] Inventor: Harold Zinnes, Rockaway, NJ.

[73] Assignee: Warner-Lambert Company, Morris Plains, NJ.

[22] Filed: June 3, 1974 [21] Appl. No.: 475,476

OTHER PUBLICATIONS Ballantine et al., J. Chem. Soc. (1957) 2229 QDl C6. Cl'emo et al., J. Chem. Soc. (1951) 700-703 QDl C6.

[4 1 July 1,1975

Primary ExaminerNorma S.-Milestone Assistant ExaminerS. D. Winters Attorney, Agent, or Firm-Albert H. Graddis; Frank S. Chow I [57] ABSTRACT An improved process for the preparation of 4-ketol,2,3,4-tetrahydrocarbazole is "disclosed. This process is as follows:

1 Claim, No Drawings which involves heating 1,3-Cyclohexanedione monophenylhydrazone (l "i o with 40% sulfuric acid. Using the described procedure, it was found that the isolation and purification of the desired product (I1) is complicated by the presence of tarryJike by-products. Thus, it is difficult to obtain satisfactory yields of pure II by this method.

The process of the present invention involves refluxing l with trifluoroacetic acid. Dilution of the reaction mixture with ice water results in precipitation of crude ll which is in a much purer state than that obtained by the literature process. The crude product is collected and easily purified by recrystallization. The yields of purified II are readily reproducible and the method is convenient for large scale preparation of this compound. This reaction may be expressed by the following scheme:

F CCO I-l 2 It is also useful as a starting material for the synthesis of 3-(morpholinomethyl)2,3-dihydrocarbazol- 4( lH)-ones which are CNS depressants (R. Littel and G. R. Allen, Jr., US. Pat. No. 3,634,420 (Jan. 11, 1972)) and for the synthesis of indolosteroids which are useful in skin graft. See J. C. Sircars and H. Zinness patent application, INDOLOSTEROIDS, filed concurrently herewith (Ser. No. 475,559).

In order to illustrate further the practice of this invention, the following examples are included.

EXAMPLE 1 1,3-Cyclohexanedione Monophenylhydrazone. To a stirred solution of g of cyclohexanedione in a mixture of 1500 ml of water and 500 ml of ethanol was added g of phenylhydrazine hydrochloride. To the resulting clear solution was added a total of 72 g of sodium acetate in small portions with vigorous stirring. The mixture was allowed to stand at room temperature and the resulting precipitate was collected, washed with water-ethanol (3:1), washed wtih a small amount of absolute ethanol, and dried in vacuo at 80 for 4 hr. Yield: 147 g, mp 184.

EXAMPLE 2 4-Keto-l ,2,3,4-tetrahydrocarbazole. A solution of 60.6 g(0.3 mole) of 1,3-cyclohexanedione monophenylhydrazone in 300 ml of trifluoroacetic acid was refluxed for three hours and poured into 2 liters of ice-water. On stirring and scratching there was obtained a solid precipitate which was collected and washed with water. The precipitate was slurried with 1000 ml of dichloromethane and the resulting insoluble crystalline solid was collected. The dichloromethane filtrate was washed with water, dried over sodium sulfate and concentrated to a volume of about 100 ml. The crystals which separated were collected, combined with the material collected earlier, and recrystallized from acetonitrile. Yield after drying in vacuo at 80 was 33 g, (59%), mp 2l8220.

I claim:

1. In an improved process for the production of a compound of the formula the improvement comprises; refluxing a compound'of the formula 

1. IN AN IMPROVED PROCESS FOR THE PRODUCTION OF A COMPOUND OF THE FORMULA 